1. Field of the Invention
The present invention relates to a method and an apparatus for detecting decrease in tire air-pressure and a program for judging decompression of a tire. More particularly, it relates to a method and apparatus for detecting decrease in tire air-pressure and a program for judging decompression of a tire with which it is possible to detect simultaneous decompression of two wheel tires of both front wheels or rear wheels.
2. Description of Background Art
An apparatus for detecting decrease in tire air-pressure (DWS) in which decompression of a tire is detected on the basis of rotational (wheel speed) information of four wheel tires attached to a vehicle is conventionally known. Such an apparatus employs a theory that a rotational velocity or a rotational angular velocity of a decompressed tire is increased when compared to remaining normal tires owing to a decrease in outer diameter (dynamic load radius of the tire) from that of a tire of normal internal pressure. In a method for detecting decrease in internal pressure on the basis of a relative difference in rotational angular velocities of tires (reference should be made to Japanese Unexamined Patent Publication No. 305011/1988),
DEL={(F1+F4)/2xe2x88x92(F2+F3)/2}/{(F1+F2+F3+F4)/4}xc3x97100(%)
is employed as a judged value DEL. Here, F1 to F4 denote rotational angular velocities of a front left tire, a front right tire, a rear left tire and a rear right tire, respectively.
However, since decompression is judged on the basis of a difference in sums of rotational angular velocities of the four wheels which are respectively located diagonally with respect to each other, it is impossible to detect simultaneous decompression of both front wheels or both rear wheels. It therefore exists the danger that fuel consumption is worsened through increase in rolling resistance of the tire and that a burst might be caused upon continuing running without being aware of decompression.
In view of the above facts, it is an object of the present invention to provide a method and an apparatus for detecting decrease in tire air-pressure and a program for judging decompression of a tire with which it is possible to detect simultaneous decompression of two wheel tires of both front wheels or both rear wheels.
In accordance with the present invention, there is provided a method for detecting decrease in tire air-pressure in which decrease in internal pressure of a tire is detected on the basis of rotational information obtained from tires attached to a vehicle. The method includes the steps of: detecting rotational information of the respective tires; storing the rotational information of the respective tires; obtaining an acceleration/deceleration of the vehicle; obtaining a slip rate when the acceleration/deceleration of the vehicle is within a specified range proximate to zero; comparing the slip rate with a slip rate which has been preliminarily obtained when the tire is under normal air pressure; and judging simultaneous decompression of both front wheel tires or simultaneous decompression of both rear wheel tires on the basis of a relationship between a value obtained through comparison of the two slip rates and a specified threshold.
Also, in accordance with the present invention, there is provided an apparatus for detecting decrease in tire air-pressure in which decrease in internal pressure of a tire is detected on the basis of rotational information obtained from tires attached to a vehicle. The apparatus includes: rotational information detecting means for detecting rotational information of the respective tires; a rotational information storing means for storing the rotational information of the respective tires; an acceleration/deceleration calculating means for obtaining an acceleration/deceleration of the vehicle; a slip rate calculating means for obtaining a slip rate when the acceleration/deceleration of the vehicle is within a specified range proximate to zero; a slip rate comparison means for comparing the slip rate with a slip rate which has been preliminarily obtained when the tire is under normal air pressure; and a decompression judging means for judging simultaneous decompression of both front wheel tires or simultaneous decompression of both rear wheel tires on the basis of a relationship between a value obtained through comparison of the two slip rates and a specified threshold.
Moreover, in accordance with the present invention, there is provided a program for judging decompression of a tire, in which for judging decrease in tire air-pressure, a computer is made to function as a rotational information storing means for storing the rotational information of the respective tires; an acceleration/deceleration calculating means for obtaining an acceleration/deceleration of the vehicle; a slip rate calculating means for obtaining a slip rate when the acceleration/deceleration of the vehicle is within a specified range proximate to zero; a slip rate comparison means for comparing the slip rate with a slip rate which has been preliminarily obtained when the tire is under normal air pressure; and a decompression judging means for judging simultaneous decompression of both front wheel tires or simultaneous decompression of both rear wheel tires on the basis of a relationship between a value obtained through comparison of the two slip rates and a specified threshold.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.